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From Paul Querna <>
Subject mod_cache_shared?
Date Sat, 11 Mar 2006 08:12:59 GMT
I have been thinking about some ideas for allowing multiple 
mod_disk_cache instances to share their cache.

There are existing 'solutions' to 'this' problem:
   - HTCP, RFC 2756,
   - ICP, RFC 2186 and RFC 2187,
   - CARP,

I've only done a quick look at each, and they all seem to be overly 
complicated.  If anyone has experience with these or other methods, 
please speak up :)

HTCP seems like the best pre-designed solution at this time.  It doesn't 
look like it got much adoption from any other proxy/cache servers. 
Anyone know why?

But, the 'lets do this quickly and make it work' part of me says, we can 
design something very simple and 'stupid', that uses the knowledge of 
how mod_cache works.

What we would do is create a new mod_cache backend, 'mod_cache_shared'.

It would run in the Quick Handler, after the other cache methods.  This 
mod_cache_shared would use some communication protocol to request this 
document from its peers.

If no peer replied in 5 ms, we would DECLINE the quick handler, and 
continue on the normal path of a cache miss. Of course, giving-up 
timeout would be configurable.

If a peer replied with 'yes we have this', we would fetch it from there, 
and *also* insert the required output filters, to add it to our local cache.



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